LT1280A/LT1281A
Low Power 5V RS232
Dual Driver/Receiver with
0.1µF Capacitors
DESCRIPTIO
The LT
®
1280A/LT1281A are dual RS232 driver/receiver
pairs with integral charge pump to generate RS232 volt-
age levels from a single 5V supply. These circuits feature
rugged bipolar design to provide operating fault tolerance
and ESD protection unmatched by competing CMOS
designs. Using only 0.1µF external capacitors, these cir-
cuits consume only 40mW of power, and can operate to
120kbaud even while driving heavy capacitive loads. New
ESD structures on the chip allow the LT1280A/LT1281A to
survive multiple
±10kV
strikes, eliminating the need for
costly TransZorbs
®
on the RS232 line pins. The LT1280A/
LT1281A are fully compliant with EIA RS232 standards.
Driver outputs are protected from overload, and can be
shorted to ground or up to
±30V
without damage. During
shutdown or power-off conditions, driver and receiver
outputs are in a high impedance state, allowing line
sharing.
The LT1281A is available in 16-pin DIP and SO packages.
The LT1280A is supplied in 18-pin DIP and SO packages
for applications which require shutdown.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TransZorb is a registered trademark of General Instruments, GSI
FEATURES
s
s
s
s
s
s
s
s
s
s
s
s
s
s
10mA Max Supply Current
ESD Protection over
±10kV
Uses Small Capacitors: 0.1µF
120kBaud Operation for R
L
= 3k, C
L
= 2500pF
250kBaud Operation for R
L
= 3k, C
L
= 1000pF
Outputs Withstand
±30V
Without Damage
CMOS Comparable Low Power: 40mW
Operates from a Single 5V Supply
Rugged Bipolar Design
Outputs Assume a High Impedance State When Off
or Powered Down
Meets All RS232 Specifications
Available With or Without Shutdown
Absolutely No Latch-up
Available in SO Package
APPLICATI
s
s
s
s
s
S
Portable Computers
Battery-Powered Systems
Power Supply Generator
Terminals
Modems
TYPICAL APPLICATI
+
0.1µF
2
4
LT1280A
17
3
5V INPUT
+
0.1µF
7
0.1µF
15
V
+
OUT
DRIVER
OUTPUT
R
L
= 3k
C
L
= 2500pF
+
0.1µF
5
6
12
V
–
OUT
RS232 OUTPUT
LOGIC
INPUTS
11
13
8
14
5k
RS232 OUTPUT
RS232 INPUT
RECEIVER
OUTPUT
R
C
L
= 50pF
LOGIC
OUTPUTS
10
18
INPUT
9
5k
16
RS232 INPUT
LT1280A • TA02
ON/OFF
LT1280A • TA01
U
UO
+
UO
Output Waveforms
1
LT1280A/LT1281A
ABSOLUTE
AXI U
RATI GS
Supply Voltage (V
CC
) ................................................ 6V
V
+
........................................................................ 13.2V
V
–
...................................................................... –13.2V
Input Voltage
Driver ........................................................... V
–
to V
+
Receiver ............................................... – 30V to 30V
ON/OFF ................................................. – 0.3V to 12V
Output Voltage
Driver ...................................... V
+
– 30V to V
–
+ 30V
Receiver .................................... – 0.3V to V
CC
+ 0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
C1
+
V
+
C1
–
C2
+
C2
–
V
–
TR2 OUT
REC2 IN
1
2
3
4
5
6
7
8
9
18 ON/OFF
17 V
CC
16 GND
15 TR1 OUT
14 REC1 IN
13 REC1 OUT
12 TR1 IN
11 TR2 IN
10 REC2 OUT
ORDER PART
NUMBER
LT1280ACN
LT1280AIN
LT1280ACSW
LT1280AISW
N PACKAGE 18-LEAD PDIP
SW PACKAGE
18-LEAD PLASTIC SO WIDE
T
JMAX
= 125°C,
θ
JA
= 80°C/ W,
θ
JC
= 36°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 90°C/ W,
θ
JC
= 26°C/W (SW)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Power Supply Generator
V
+
Output
V
–
Output
Supply Current (V
CC
)
Supply Current When OFF (V
CC
)
Supply Rise Time
Shutdown to Turn-On
ON/OFF Pin Thresholds
ON/OFF Pin Current
Oscillator Frequency
Driver
Output Voltage Swing
Logic Input Voltage Level
CONDITIONS
(Note 2)
MIN
TYP
7.9
– 7.0
8
q
q
(Note 3), T
A
= 25°C
Shutdown (Note 4) LT1280A Only
C1 = C2 = C3 = C4 = 0.1µF
LT1280A Only
Input Low Level (Device Shutdown)
Input High Level (Device Enabled)
0V
≤
V
ON/OFF
≤
5V
Load = 3k to GND
Input Low Level (V
OUT
= High)
Input High Level (V
OUT
= Low)
2
U
U
W
W W
U
W
(Note 1)
Short-Circuit Duration
V
+
................................................................... 30 sec
V
–
................................................................... 30 sec
Driver Output .............................................. Indefinite
Receiver Output .......................................... Indefinite
Operating Temperature Range
LT1280AC/LT1281AC ............................. 0°C to 70°C
LT1280AI/LT1281AI .......................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
C1
+
1
V
+
2
C1
C2
C2
–
+
–
16 V
CC
15 GND
14 TR1 OUT
13 REC1 IN
12 REC1 OUT
11 TR1 IN
10 TR2 IN
9
REC2 OUT
ORDER PART
NUMBER
LT1281ACN
LT1281AIN
LT1281ACSW
LT1281AISW
3
4
5
V
–
6
TR2 OUT 7
REC2 IN 8
N PACKAGE 16-LEAD PDIP
SW PACKAGE
16-LEAD PLASTIC SO WIDE
T
JMAX
= 125°C,
θ
JA
= 90°C/ W,
θ
JC
= 46°C/W (N)
T
JMAX
= 125°C,
θ
JA
= 95°C/ W,
θ
JC
= 27°C/W (SW)
MAX
UNITS
V
V
mA
mA
µA
ms
ms
V
V
µA
kHz
V
V
V
V
q
q
q
0.8
– 15
1
0.2
0.2
1.2
1.6
130
10
14
10
2.4
80
Positive
Negative
q
q
q
q
5.0
7.5
– 6.3
1.4
1.4
– 5.0
0.8
2.0
LT1280A/LT1281A
ELECTRICAL CHARACTERISTICS
PARAMETER
Logic Input Current
Output Short-Circuit Current
Output Leakage Current
Data Rate (Note 7)
Slew Rate
Propagation Delay
Receiver
Input Voltage Thresholds
CONDITIONS
0.8V
≤
V
IN
≤
2.0V
V
OUT
= 0V
(Note 2)
MIN
q
TYP
5
17
10
MAX
20
100
UNITS
µA
mA
µA
kBaud
kBaud
±9
q
Shutdown V
OUT
=
±30V
(Note 4)
R
L
= 3k, C
L
= 2500pF
R
L
= 3k, C
L
= 1000pF
R
L
= 3k, C
L
= 51pF
R
L
= 3k, C
L
= 2500pF
Output Transition t
HL
High-to-Low (Note 5)
Output Transition t
LH
Low-to-High
Input Low Threshold (V
OUT
= High)
Input High Threshold (V
OUT
= Low)
Input Low
Input High
V
IN
=
±10V
Shutdown (Note 4) 0
≤
V
OUT
≤
V
CC
Output Low, I
OUT
= – 1.6mA
Output High, I
OUT
= 160µA (V
CC
= 5V)
Sinking Current, V
OUT
= V
CC
Sourcing Current, V
OUT
= 0V
Output Transition t
HL
High-to-Low (Note 6)
Output Transition t
LH
Low-to-High
C Grade
C Grade
I Grade
I Grade
120
250
4
15
7
0.6
0.5
q
q
q
q
q
q
q
q
30
1.3
1.3
V/µs
V/µs
µs
µs
V
V
V
V
V
kΩ
µA
V
V
mA
mA
ns
ns
0.8
0.2
0.1
3
1.3
1.7
1.3
1.7
0.4
5
1
0.2
4.2
– 20
20
250
350
2.4
3.0
1.0
7
10
0.4
– 10
600
600
Hysteresis
Input Resistance
Output Leakage Current
Output Voltage
Output Short-Circuit Current
Propagation Delay
3.5
10
The
q
denotes specifications which apply over the operating temperature
range (0°C
≤
T
A
≤
70°C for commercial grade, and – 40°C
≤
T
A
≤
85°C for
industrial grade.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
Testing done at V
CC
= 5V and V
ON/OFF
= 3V, unless otherwise
specified.
Note 3:
Supply current is measured as the average over several charge
pump cycles. C
+
= C
–
= C1 = C2 = 0.1µF. All outputs are open, with all
driver inputs tied high.
Note 4:
Supply current measurements in shutdown are performed with
V
ON/OFF
≤
0.1V.
Note 5:
For driver delay measurements, R
L
= 3k and C
L
= 51pF. Trigger
points are set between the driver’s input logic threshold and the output
transition to the zero crossing (t
HL
= 1.4V to 0V and t
LH
= 1.4V to 0V).
Note 6:
For receiver delay measurements, C
L
= 51pF. Trigger points are
set between the receiver’s input logic threshold and the output transition
to standard TTL/CMOS logic threshold (t
HL
= 1.3V to 2.4V and t
LH
= 1.7V
to 0.8V).
Note 7:
Data rate operation guaranteed by slew rate, short-circuit current
and propagation delay tests.
TYPICAL PERFOR A CE CHARACTERISTICS
Driver Maximum Output Voltage
vs Load Capacitance
8.0
7.5
PEAK OUTPUT VOLTAGE (V)
DRIVER OUTPUT VOLTAGE (V)
PEAK OUTPUT VOLTAGE (V)
7.0
20k BAUD
6.5
60k BAUD
6.0
5.5
5.0
0
1
2
3 4 5 6 7 8
LOAD CAPACITANCE (nF)
9
10
120k BAUD
U W
LT1280A • TPC01
Driver Minimum Output Voltage
vs Load Capacitance
–4.0
–4.5
120k BAUD
–5.0
60k BAUD
–5.5
–6.0
–6.5
–7.0
0
1
2
3 4 5 6 7 8
LOAD CAPACITANCE (nF)
9
10
20k BAUD
10
8
6
4
2
0
–2
–4
–6
–8
Driver Output Voltage
R
L
= 3k
V
CC
= 5.5V
V
CC
= 5V
V
CC
= 4.5V
OUTPUT HIGH
OUTPUT LOW
V
CC
= 4.5V
V
CC
= 5V
V
CC
= 5.5V
–10
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
LT1280A • TPC02
LT1280A • TPC03
3
LT1280A/LT1281A
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Input Thresholds
3.00
2.75
THRESHOLD VOLTAGE (V)
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
INPUT LOW
INPUT HIGH
THRESHOLD VOLTAGE (V)
2.50
SUPPLY CURRENT (mA)
Supply Current
25
100
SHORT-CIRCUIT CURRENT (mA)
20
LEAKAGE CURRENT (
µA)
SUPPLY CURRENT (mA)
2 DRIVERS LOADED R
L
= 3k
15
1 DRIVER LOADED R
L
= 3k
10
NO LOAD
5
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
Receiver Short-Circuit Current
50
16
14
SHORT-CIRCUIT CURRENT (mA)
40
SLEW RATE (V/µs)
30
20
10
0
–55 –25
50
25
0
75
TEMPERATURE (°C)
4
U W
LT1280A • TPC04
Supply Current vs Data Rate
50
2 DRIVERS ACTIVE
R
L
= 3k
C
L
= 2500pF
3.0
2.5
2.0
1.5
1.0
ON/OFF Thresholds
40
30
ON THRESHOLD
20
OFF THRESHOLD
0.5
0
–55 –25
10
0
0
25
50
75
100
DATA RATE (kBAUD)
125
150
50
25
75
0
TEMPERATURE (°C)
100
125
LT1280A • TPC05
LT1280A • TPC06
Driver Leakage in Shutdown
30
25
20
15
Driver Short-Circuit Current
I
SC+
10
1
V
OUT
= 30V
V
OUT
= –30V
I
SC–
10
5
0
–55 –25
100
125
0.1
–55 –25
50
25
0
75
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
LT1280A • TPC07
LT1280A • TPC08
LT1280A • TPC09
Slew Rate vs Load Capacitance
RX I
SC–
RX I
SC+
12
10
8
+SLEW
6
–SLEW
4
2
100
125
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
LOAD CAPACITANCE (nF)
LT1280A • TPC11
LT1280A • TPC10
LT1280A/LT1281A
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown to Driver Outputs
10V
DRIVER 1
OUTPUT
5V
GND
GND
DRIVER 2
OUTPUT
– 5V
– 10V
ON/OFF PIN
INPUT
LT1280A • TPC12
LT1280A • TPC13
PI FU CTIO S
V
CC
:
5V Input Supply Pin. This pin should be decoupled
with a 0.1µF ceramic capacitor close to the package pin.
Insufficient supply bypassing can result in low output
drive levels and erratic charge pump operation.
GND:
Ground Pin.
ON/OFF:
A TTL/CMOS Compatible Operating Mode Con-
trol. A logic low puts the LT1280A in shutdown mode.
Supply current drops to zero and both driver and receiver
outputs assume a high impedance state. A logic high fully
enables the device.
V
+
:
Positive Supply Output (RS232 Drivers). V
+
≈
2V
CC
–
1.5V. This pin requires an external charge storage capaci-
tor C
≥
0.1µF, tied to ground or V
CC
. Larger value capaci-
tors may be used to reduce supply ripple. With multiple
transceivers, the V
+
and V
–
pins may be paralleled into
common capacitors.
Negative Supply Output (RS232 Drivers).
≈
–
(2V
CC
– 2.5V). This pin requires an external charge storage
capacitor C
≥
0.1µF. Larger value capacitors may be used
to reduce supply ripple. With multiple transceivers, the V
+
and V
–
pins may be paralleled into common capacitors.
V
–
:
V
–
TR1 IN, TR2 IN:
RS232 Driver Input Pins. These inputs are
TTL/CMOS compatible. Inputs should not be allowed to
float. Tie unused inputs to V
CC
.
TR1 OUT, TR2 OUT:
Driver Outputs at RS232 Voltage
Levels. Driver output swing meets RS232 levels for loads
up to 3k. Slew rates are controlled for lightly loaded lines.
U W
Driver Output Waveforms
DRIVER OUTPUT
R
L
= 3k
C
L
= 2500pF
DRIVER OUTPUT
R
L
= 3k
U
U
U
Output current capability is sufficient for load conditions
up to 2500pF. Outputs are in a high impedance state when
in shutdown mode or V
CC
= 0V. Outputs are fully short-
circuit protected from V
–
+ 30V to V
+
– 30V. Applying
higher voltages will not damage the device if the overdrive
is moderately current limited. Short circuits on one
output can load the power supply generator and may
disrupt the signal levels of the other outputs. The driver
outputs are protected against ESD to
±10kV
for human
body model discharges.
REC1 IN, REC2 IN:
Receiver Inputs. These pins accept
RS232 level signals (±30V) into a protected 5k terminat-
ing resistor. The receiver inputs are protected against ESD
to
±10kV
for human body model discharges. Each receiver
provides 0.4V of hysteresis for noise immunity. Open
receiver inputs assume a logic low state.
REC1 OUT, REC2 OUT:
Receiver outputs with TTL/CMOS
Voltage Levels. Outputs are in a high impedance state
when in shutdown mode to allow data line sharing. Out-
puts are fully short-circuit protected to ground or V
CC
with
the power ON, OFF or in the shutdown mode.
C1
+
, C1
–
, C2
+
, C2
–
:
Commutating Capacitor Inputs.
These pins require two external capacitors C
≥
0.1µF: one
from C1
+
to C1
–
and another from C2
+
to C2
–
. C1 should
be deleted if a separate 12V supply is available and
connected to pin C1
+
. Similarly, C2 should be deleted if a
separate – 12V supply is connected to pin V
–
.
5
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